There are two major prior art approaches to switching or re-arranging the connections between high-bandwidth signals. These existing solutions include the use of optical-electrical-optical (OEO) switches and the use of pure optical switches.
Optical-Electronic-Optical (OEO) Approach
The optical-electronic-optical (OEO) approach converts incoming optical signals to electronic form, switches (i.e., rearranges) the signals electronically, and then converts the electrical signals back to optical form. The building blocks for such an approach are electronic crossbar switch integrated circuits (ICs), which are relatively inexpensive. However, the use of these electronic crossbar switch integrated circuits does have some disadvantages. First, the electronic crossbar switches have a limited capacity. The capacity is typically limited to the number of ports multiplied by the data rate per port. Second, the electronic crossbar switches consume significant amounts of power.
Moreover, high-capacity OEO switches typically require multi-stage networks because of the limited size of the building blocks. As can be appreciated, these multi-stage networks become physically large, consume large amounts of power, and once the networks reach a certain size require expensive optical interconnects between stages.
Consequently, at some capacity, the OEO switches lose viability and all-optical switches become attractive.
All-Optical Approach
An all-optical switch is a switch that has optical inputs, optical outputs, and no intermediate optical-electronic-optical conversion. One example of an all-optical switch is a crossbar optical switch. The publication entitled, “Compact optical cross-connect switch based on total internal reflection in a fluid-containing planar lightwave circuit,” by J. E. Fouquet, paper TuM1, Conference on Optical Fiber Communications, OFC 2000, Baltimore Md., USA, pp. 204–206, describes the crossbar optical switch that employs a large number of very simple 1×2 and 2×2 switches. However, one significant disadvantage of the crossbar optical switch is that the optical loss scales linearly with the number of ports. Consequently, the crossbar optical switch is limited by the total number of ports required.
Another example of an all-optical switch is a “fan-out, fan-in” optical switch. The publication entitled, “1296-port MEMS transparent optical crossconnect with 2.07 Petabit/s switch capacity,” by R. Ryf et al., paper PD28, Conference on Optical Fiber Communications, OFC 2001, Anaheim Calif., USA, describes an exemplary “fan-out, fan-in” optical switch. “Fan-out, fan-in” optical switches have a plurality of single mode fibers as inputs and a plurality of single mode fibers as outputs. A 1×N optical switch that is associated with each input directs light to the N×1 optical switch associated with the desired output. Typically, these “fan-out, fan-in” optical switches employ optics to perform the interconnection in free space.
One disadvantage of these types of optical switches is that very precise alignment of the optical system is required to steer beams of light from a single-mode fiber input to a single-mode fiber output with acceptable loss. First, the beams of light must be steered to hit a very small target area of a single mode fiber output. Second, not only must the light hit the small target area, but the light must also arrive at the target within a particular range of angles. If either of these two conditions is not met, the loss may become unacceptable.
For example, typically a very sophisticated closed-loop control is required to achieve and maintain the needed optical alignment. The closed-loop control has components, such as an optical source and coupler for each input port, an optical detector and splitter for each output port, and a sophisticated electronic signal processing circuit for each connection. As can be appreciated, the need for this sophisticated closed-loop control approach increases the complexity of switch design that may result in higher costs to manufacture the switch and that may pose reliability concerns.
Consequently, it is desirable for there to be a switching fabric for use in optical cross-connects that simplifies the optical system needed and relaxes the optical alignment requirements, thereby reducing the complexity and costs associated with the manufacture of such a switch.
Based on the foregoing, there remains a need for an optical switching fabric with an optical to electrical converter in the output plane that overcomes the disadvantages set forth previously.